NVFS explanation

The new feature on T5/T650 devices is the use of the flash memory or — expressed more technically — NVFS, Non-Volatile File Storage.

Technically speaking, NVFS is a file system that stores the files similarly to a card. However, NVFS basic advantage (and reason of being) is that it preserves the data also after the total power discharge.

NVFS databases can't be accessed directly. Therefore Palm OS reserves part of RAM called DbCache.

Prior to its use the databases are copied from NVFS to the DbCache and after the use they are copied back (if changed).

DbCache gets subsequently filled because the databases are not immediately purged from the DbCache, but (for performance reasons) stay in the cache as long as there is enough space.

On T5 the DbCache has 10 MB and it is considered full when the free space reaches approx. 1MB.

Full DbCache means slower data operations because of the increased data exchange between the NVFS and the DbCache.

However, the user will generally notice it only when a large amount of data is processed. (Such as e.g. backup of the whole memory.)

DbCache can be emptied only via reset.

There is another important difference:

NVFS has different granularity than the conventional RAM with the lowest accessible unit being 512 By.

The consequence is that the databases with small records (e.g. contacts) will occupy much more space on NVFS than they used to have on the RAM-based systems.

Many applications have real problems to adapt to this situation.

Example:
Database record with 50 By length will occupy 512 By on the NVFS.
A database with 2000 such records will occupy 100K in the dynamic RAM, but 1 MB in NVFS.

Remark:
Newer Palm models came with substantially smaller record size and this problem was thus virtually avoided.

NVFS Bugs

It is known fact that the NVFS implementation is not reliable. As a rule, the problems manifest when the DbCache is full.

Our stress tests indicated that certain Palm OS services for the database access fail in 0.1% cases when the DbCache is full. There exist workarounds for most of the cases - unfortunately not for all. (E.g. when Palm OS itself uses these services.)

Palm policy is remarkable - unofficially they admitted the problems and a patch for T650 should be on the way.

However, the T5 may stay as it is. (Unofficial information valid as of Mar-14.)

Useful advices

Take advantage of the information collected by other users.
E.g. this discussion contains very interesting information about the stability of various apps on the T5.

Special danger comes from the background applications that cannot work around the NVFS bugs.

These apps work as a rule reliably until more intensive data operations are performed on the full DbCache.

The peculiar thing is that the user will see crashing the application running in the foreground, (Typical examples are mysterious crashes during the HotSync or crashes of the backup programs.)

Another way how to deactivate the background applications is the warm reset. (Reset while the Up key is being pressed.)

Special on this reset is that it does not send any notifications that are otherwise used to start running the background applications. Roughly speaking, warm reset starts only the basic OS services without the 3rd party additions.

Buggy background apps

Although there are many more, here are just a few popular apps that use to crash:

• ClipPRO 2.1.1
• TextPlus 5.6
• Okey 1.2.3